We just bought a Mull F28 sloop, 1987. When operating the electric bilge pump, the discharge is filling the shower sump. If the shower sump us not energized, it overflows back into the bilge. We realized this after overfilling the water tanks. Any input on how this should work?Thanks

I’ll give this a shot - I have the f35 pedrick so more than likely its all different. Usually I believe the bilge will discharge overboard - shower sump will discharge overboard. Trace your bilge Manuel and electric hoses. Trace the sump hose - that one should be 1/2”. PO May have taken a short cut perhaps in routing hoses.... let us know what you find.

Some more tracing yesterday. It appears the two pumps' discharge hoses are teed to a single hose that rises to a loop and then leads to the thru hull. The bilge pump looks like it has a backflow preventer valve. It appears the shower sump does not. Water from the bilge pump may be taking the path of least resistance and flowing into the shower sump, instead of continuing uphill to the loop. Since I cannot see the water entering the sump, I can only assume that it is entering via the discharge. Perhaps both pumps had preventers in the past and the PO removed a failed one from the sump without realizing the consequence. I will install a new one and see if that helps.

Another Mull F-28 owner here who had a similar issue. On my cruise this year I had two mornings in a row where I woke to find the bilge filled with water up to the cabin sole. I had left the shower sump on since I was using the icebox, which drains into the sump, and I thought that would keep it drained. Somehow that was causing a backflow from the drain line that goes to the forward through-hull. I ended up just removing the whole sump assembly since I will never use the shower anyway, and plugging the drain line. Easier to keep the bilge dry and clean now.

It was, indeed, the check valve on the sump. Having sat fouled for a period of time caused the flapper to become distorted and non-functional. Replaced with a Whale duckbill non-return valve, cleaned the entire bilge and sump. Mini wet/dry vacuums work wonders for drying out bilges. All good now except the bilge pump wiring. Should there be available, in the bilge area, a constant hot 12v wire for the float switch? I don’t like having to leave the dc panel and bilge switch on when leaving the boat.